By conservative estimate, Attention-Deficit Hyperactivity Disorder (ADHD) is a common disorder that occurs in at least 3 to 6% of school-aged children (Barkley, 1990). It is marked by symptoms of inattention and hyperactive-impulsive behavior that are developmentally inappropriate. These symptoms must occur in multiple settings and impair functioning to a clinically significant degree (DSM-IV; American Psychiatric Association, 1994). ADHD is believed to be a developmental disorder that begins in early childhood, which distinguishes it from disorders of attention and behavioral control that arise later as consequence of brain injury. Although ADHD was once thought to affect only children, considerable evidence has accumulated to show that ADHD frequently continues into adulthood. Approximately 60% of ADHD youth (about 3-4% of all adults) have clinically significant residual problems as adults (Faraone, 1999; Hechtman, 2000; Mannuzza & Klein, 1999). Although inattention problems appear to persevere into adulthood unchanged, studies suggest that some persons' ADHD hyperactive/impulsive symptoms diminish following teenage years. However, the mechanism for this decrease is not currently known (Wender, 1987; Weiss & Hechtman, 1986, 1993; Brown, 1995).